Disclosed herein is a nanosilver ink composition. More particularly, disclosed herein is a nanosilver ink composition comprising silver nanoparticles; polystyrene; and an ink vehicle.
Xerox Corporation has invented a nanosilver particle which is stabilized by an organoamine. U.S. Pat. No. 8,765,025, which is hereby incorporated by reference herein in its entirety, describes a metal nanoparticle composition that includes an organic-stabilized metal nanoparticle and a solvent in which the solvent selected has the following Hansen solubility parameters: a dispersion parameter of about 16 MPa0.5, or more, and a sum of a polarity parameter and a hydrogen bonding parameter of about 8.0 MPa0.5 or less. U.S. Pat. No. 7,270,694, which is hereby incorporated by reference herein in its entirety, describes a process for preparing stabilized silver nanoparticles comprising reacting a silver compound with a reducing agent comprising a hydrazine compound by incrementally adding the silver compound to a first mixture comprising the reducing agent, a stabilizer comprising an organoamine, and a solvent.
U.S. patent application Ser. No. 13/866,704, which is hereby incorporated by reference herein in its entirety, describes stabilized metal-containing nanoparticles prepared by a first method comprising reacting a silver compound with a reducing agent comprising a hydrazine compound by incrementally adding the silver compound to a first mixture comprising the reducing agent, a stabilizer comprising an organoamine, and a solvent. U.S. patent application Ser. No. 14/188,284, which is hereby incorporated by reference herein in its entirety, describes conductive inks having a high silver content for gravure and flexographic printing and methods for producing such conductive inks.
Inks have been successfully formulated in non-polar solvents such as decalin and bicyclohexyl and successfully printed using inkjet printing technologies. As printed electronics matures and moves to higher volume production, it is desirable to have inks that can be used in offset printing technologies such as flexography and gravure. Offset printing technologies provide ready established printing processes and equipment. FIG. 1 shows a schematic diagram of a flexographic printing process. Flexographic printing processes generally comprise the following steps: a) anilox roller 100 having metered anilox cells 112 picks up ink from the ink pan 114; b) doctor blade 116 scrapes off excess ink; c) ink is then deposited on to the flexo-plate 118; d) flexo plate 118 and plate cylinder 120 transfer features onto the substrate (material web) 122 shown exiting impression cylinder 124.
A gravure printing process is very similar to flexography except that it does not have an anilox roller and the image is engraved onto a metal cylinder. This makes gravure more expensive than flexo and high volume printing. One of the main advantages of gravure over flexo is the ability to consistently make high quality prints. FIG. 2 shows a schematic diagram of a gravure printing process. Gravure processes generally comprise the following steps: a) plate 200 comprising plate cylinder 212 picks up ink 214 from the ink pan; b) doctor blade 216 scrapes off excess ink; c) ink is then transferred from the plate cylinder 212 to the substrate (paper) 218 shown exiting impression cylinder 220 having printed image 222 printed thereon.
Current inks include high loadings of silver nanoparticles, such as from about 50 to about 70 percent. Such inks have a very low viscosity, such as from about 8 to about 12 centipoise and typically greater than about 10 centipoise.
Gravure and flexographic processes provide a potentially efficient way to manufacture a number of conductive components at a lower cost than that of other printing applications. However, when used for flexographic printing, the low viscosity of current ink compositions results in very thin films, such as less than about 500 nanometers, and a minimum line width of about 125 nanometers. Thin, highly conductive films are good for certain applications such as memory devices.
However, there are a number of applications that require thicker films, such as RFID (Radio Frequency Identification) antennas which require a film having a thickness of about 10 to about 20 micrometers. When low viscosity ink is used in gravure printing processes, the ink overspreads. Higher viscosity ink is desired to print thicker films and to improve line resolution for flexographic printing and to prevent smearing for gravure printing. The current method for increasing ink viscosity is to increase silver loading, such as to about 65 to about 75 percent. However, this is a costly solution which does not provide an adequate increase to ink viscosity.
A need remains for an improved ink composition that can provide an adequate ink viscosity without negatively impacting ink performance. Further, a need remains for inks that can be successfully employed in offset technologies for printed electronics applications. Further, a need remains for inks that can be successfully employed in offset technologies for printed electronics applications including gravure and flexographic printing processes.
The appropriate components and process aspects of the each of the foregoing U.S. Patents and Patent Publications may be selected for the present disclosure in embodiments thereof. Further, throughout this application, various publications, patents, and published patent applications are referred to by an identifying citation. The disclosures of the publications, patents, and published patent applications referenced in this application are hereby incorporated by reference into the present disclosure to more fully describe the state of the art to which this invention pertains.